Currently, there are many commercially available Chinese patent medicines or healthcare foods that promise to solve the problem of insomnia, which is also declared to be composed of pure plant or pure traditional Chinese medicine, do not contain Western medicine used to treat sleep problems or hormones.
Melatonin, also known chemically as N-acetyl-5-methoxytryptamine, is a kind of indoleamine hormone secreted by the pineal gland located in the human brain. Known as the “hormone of darkness”, melatonin secretion decreases with increasing intensity of light. Melatonin is mainly used to regulate sleep-wake cycle and physiological circadian rhythms. Melatonin also has anti-aging properties.
Melatonin is a kind of endogenous hormone. Some studies have shown that heavy use of melatonin may cause breathing problems and hangover effect. Meanwhile, melatonin may impact on some sedative hypnotic drug's efficacy, such as clonazepam. In Europe, dosage interval, target population and dosage are all strictly restricted. In the US, melatonin can be sold in the form of dietary supplements. The label must include content and dosage instructions. In China, melatonin is used as healthcare food. There are clear legal provisions: daily dosage restriction of melatonin is 1-3 mg; no ingredients can be added except vitamin B6; the section of “warning” should tell the people who engage in mechanical work or dangerous operation not to use before they work/while they are working; meanwhile, it should also tell the people having autoimmune disease (rheumatism, etc.) or hyperthyroidism disease to use with caution. Thus, melatonin should be consumed according to doctor's advice. The dosage must be confirmed. Melatonin should be used with more caution in children. However, due to good sedative hypnotic effect of melatonin and complex ingredients of Chinese patent medicine and healthcare food, some unscrupulous people add melatonin to sedative hypnotic Chinese patent medicine or healthcare food illegally. They hype the effect of the products in order to drive up prices. It makes users not clearly aware of their dosage, thus causing adverse consequences and harm to the people's health. Especially in some rural area and underdeveloped small cities, lack of necessary testing equipment and weak technical regulation has created opportunities for criminals to employ trickery, resulting in a large number of counterfeit or substandard drugs, causing confusion in the market of traditional Chinese medicine and healthcare food.
The existing methods for detecting whether there is melatonin added to sedative hypnotic Chinese patent medicine or healthcare food mainly include the following four methods:
1. Thin Layer Chromatography (TLC)
The component to be tested is extracted from samples with methanol. A small spot of test solution is applied to a silica gel plate, as well as reference solution. Developing agent is used to develop the plate. Then the plate is taken out, dried, and inspected under ultraviolet lamp at 254 nm. With the help of developing agent, different substances appear at different TLC plate position in the form of spot due to the differences in migration rates. The presence of target components in the samples can be determined by the experimental results that the spot of test sample appears at the same position as the reference. If spot appears on TLC chromatogram of test solution is at the same position as melatonin reference solution, it may indicate the presence of melatonin in the test sample.
Advantage of TLC is free of expensive analytical instrument. Disadvantages are: (1) Low in resolution; traditional Chinese medicine are complex, there are a lot of interference. Some coexisting components can be easily mistaken for melatonin If some coexisting components are in a large amount and chromatographic shift value is close to that of the component to be tested, the detection of target components may be interfered. (2) It takes long time to develop and dry, which fails to meet the requirement of rapid measurement. (3) TLC plate needs to be dried and stored in dry place. Environment temperature and humidity have a great effect on separation. (4) Require fixed location. Not suitable for mobile on-site detection. (5) Require tester with rich experience
2. High Performance Liquid Chromatography (HPLC)
HPLC is commonly used modern analytical method. Under the same chromatographic conditions, different materials have different retention time. Under the same chromatographic conditions, melatonin reference solution and test solution extracted from the sample are injected separately. According to the retention time of chromatographic peak, it can be determined whether the test sample contains melatonin components.
Advantages of HPLC chromatography is high efficiency and high sensitivity. Disadvantages are: (1) The equipment is expensive; it takes long time for pretreatment of sample; the column is vulnerable to be polluted; high cost; (2) It is easy to make a mistake in judgment when the peak retention time of some coexisting components is close to that of melatonin; (3) Instrument has high requirements to the environment, a fixed location is required; not suitable for mobile on-site detection.
3. High Performance Liquid Chromatography—Mass Spectrography (HPLC-MS)
HPLC-MS, using HPLC as separator, mass spectrography as analyzer, is suitable to analyze complex composition, even in the case of serious interference. This analytical method can improve the reliability of the test results.
HPLC-MS is an analytical method, costing more and being more complex than HPLC. Instrument has higher requirements to the environment. Instrument needs to be fixed, and is not suitable for mobile on-site detection. These detections can only be performed in a few laboratories, so it is difficult to promote.
In the field of Chinese patent medicine and healthcare food, the method for rapidly screening melatonin by physical and chemical reaction has not been reported yet. For drugstore and grassroots drug test department, it is very necessary to develop a method for rapidly screening melatonin adulteration of Chinese patent medicine or healthcare food. It will help on-site detection and provide evidence timely for regulation of Chinese patent medicine or healthcare food. It is useful to combat counterfeiting and protect the medication safety of the people.